1. Field of the Invention
The present invention relates to a method for detoxifying flue gas containing hexachlorodisilane (hereinafter referred to as “HCD”) for deposition that is discharged from a CVD (chemical vapor deposition) apparatus in the production of semiconductors, and to a detoxifying apparatus therefor.
2. Description of the Related Art
Flue gas containing several substances is discharged from a CVD apparatus, which is a silicon wafer production equipment. Some of the substances are explosive or toxic, and the flue gas needs to be detoxified before being released into the atmosphere. A detoxifying apparatus is connected to the CVD apparatus, and is for detoxifying the flue gas containing a toxic substance discharged from the CVD apparatus. JP H11-33345A discloses such the apparatus.
Gases used in the CVD apparatus are classified according to usage, e.g., for deposition, for cleaning, for etching and the like, and there are several types of gases depending on use. HCD has been newly developed as deposition gas.
HCD is represented by the chemical formula “Si2Cl6”. When HCD is subjected to a hydrolysis reaction at room temperature, silico-oxalic acid (reactive silica, chemical formula: (SiOOH)2) is formed. The silico-oxalic acid is explosive and is an extremely dangerous substance.Si2Cl6+4H2O→(SiOOH)2+6HCl  Formula 1
On the other hand, when HCD is subjected to thermolysis in the absence of water (hereinafter referred to as nonaqueous), the following reactions occur:
(a) Nonaqueous•anaerobic: 2Si2Cl6→3SiCl4+Si
(b) Nonaqueous•aerobic: Si2Cl6+2O2→2SiO2+3Cl2 
When Si2Cl6 is subjected to thermolysis in the presence of oxygen, chlorine is generated as shown in (b). Then the chlorine corrodes a detoxifying apparatus (1). To prevent chlorine generation, a certain amount of moisture is required, but if there is an excessive amount of water, silico-oxalic acid is generated as described above.